Assisted petroleum recovery by selective combustion in multi-bedded reservoirs



R. F. MELDAU ETAL 3,159,215

MBUsTIoN Dec. 1, 1964 ASSISTED PETROLEUM RECOVERY BY SELECTIVE CO INMULTI-BEDDED RESERVOIRS 4 Sheets-Sheet l Filed Sept. 25, 1958 .5.. SMM,

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||UUM IBH Q zfwx Dec. 1, 1964 R F MELDAU ETAL 3,159,215

ASSISTED PETROLEM ECOVERY BY SELECTIVE GOMBUSTION IN MULTI-BEDDEDRESERVOIRS Filed Sept. 23, 1958 4 SheeCS-Sheel'l 2 INVENTRS ROBERT EMELD/w ./oH/v McK//v/vE/.L

DCC l, 1964 R. F. MELDAU ETAL 3,159,215

ASSISTED PETROLEUM RECOVERY BY SELECTIVE COMBUSTION IN MULTI-BEDDEDRESERVOIRS Filed sept. 2s, 1958 4 sheets-sheet s TO SEPARATOR FUEL GAS 4WATER INVENTORS ROBERT F. MELD/1U JOHN C. McK/NNELL R. F. MELDAU ETALRECOVER Dec. l, 1964 3,159 TIoN ASSISTED PETROLEUM Y BY SELECTIVE COMBUSIN MULTI-BEDDED RESERVOIRS 4 Sheets-Sheet 4 Filed Sept. 25, 1958REDUCTION OF OIL/WATER VISCOSITY RATIO WITH TEMPERATURE INCREASE OOO 20o25o TEMPERATURE- F.

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um SMN Ram E mum I N R Erc .m VR NMM M .|00 R J Y B 4 G F United StatesPatent Office y aisazls Patented Dec. l, 1964 3,159,215 ASSSTED PETRLEUMREQUVERY BY SELEC- 'HVE CQWUS'HON EN MULTl-EEDDED RESER- VHS Robert F.Meldau, Whittier, and .lohn C. McKinneil, Taft, Calif., assignors toCalifornia Research Corporation, San Franeisco, Calif., a corporation ofDelaware Filed Sept. 23, i953, Ser. No. 762,818 Claims. (Cl. 16o-10) Thepresent invention relates to assisted oil recovery methods. Moreparticularly, it relates to an improved method of assisting recovery ofoil from an underground reservoir by consecutively and simultaneouslyinjecting thermal energy to selected portions of the reservoir.

It is `an object of the present invention to increase the recovery ofpetroleum from an underground reservoir that comprises a series ofoil-permeable zones coutaining mobile oil separated by relatively thin,impermeable zones, such as sandstone formations that have shale or otheruid barriers between said members. The method of the invention isspecifically useful where more than one Huid-impermeable zone separatesseveral oil-bearing zones. However, the method is also useful in anyreservoir where the fluid-permeable, e.g., sand, zones are sutlicientlyisolated from each other to permit wells penetrating them to be sealedor packed-off from each other.

In assisted oil recovery, frequently referred to as secondary recoveryof oil from an underground reservoir, it has been proposed to ignite anoil-producing formation and then supply a critical amount of oxygen inthe form of compressed air to that formation to form a coinbustion4front that both heats the oil and generates gas to force oil to flowfrom the air injection well toward a fluid-producing well. In practice,it has been found that it is diflicult to ignite and `maintaincombustion in reservoirs such as those encountered in California and theGulf Coast area where oil-producing zones frequently comprise aplurality of oil-producing zones that are formed of sand and areinterlaminated by shale beds that lie parallel to the sand beds. One ofthe reasons for this diiiiculty is the differences in fluid permeabilityof the various oilproducing zones. Where these differences exist, theairand combustion will preferentially occur in the zone of greatestpermeability (the path of least resistance to ilow). Additionally, thecost of an assisted oil recovery project using all air as the injectioniluid has been found to be more expensive than conventional waterflooding operations, since the investment in air compressor horsepower,as compared to equivalent water pump capacity, is relatively great.While this added cost is justified by the greater recovery of oil usinga combustion drive, as compared to a water drive, the oil-bearing zonemust be thick and relatively uniform in permeability to obtain maximumbenefit. However, when the oil zone is relatively thin or non-uniform inpermeability, We have found that much of the heat generated by thecombustion process is lost to the overlying and underlying shale andsand zones.

In accordance with a preferred method of carrying out the presentinvention, one of the more permeable, oil-bearing zones in a series ofmultiple zones is packed off in an injection well so that oxygen, in theform of air, can be pumped into that zone to ignite and continuecombustion therein. When the invention is practiced in a pair ofpermeable oil-bearing zones, it is preferred to initiate combustion inthe more iluid permeable zone if one of the zones has a greaterpermeability to fluid ilow than the other. The fluid-impermeable zoneseither overlying or underlying this rst oil-bearing zone preventvertical flow of iluids to adjacent oil zones. Suicient air is thensupplied to this middle zone to maintain combustion of a part of thehydrocarbon iluid so that the burning front is progressively advancedaway from said injection well an adequate distance through theoilbearing zone tow-ard one or more production wells. In advancing thecombustion front, the overlying and underlying shale and sand bodies areprogressively heated by conduction losses from the combustion front andform a heat reservoir that extends from near the injection well to thecombustion front. After the combustion front has been advanced in thisway, a drive liquid, such as water, conveniently supplied at surfacetemperatures is pumped into the adjacent heated oil-bearing zones. Whereoil-producing zones both overlie and underlie the combustion zone, watermay be pumped into both the overand underlying beds. The water thussupplied moves into a heated oil bearing strata and both the displacingwater and the displaced oil -are progressively heated as they movetogether from the injection well toward the producing well.

The progressively heated oil in the overlying and underlying beds isdisplaced by the heated Water in a more efiicient manner than if the oiland water were at normal formation temperature. -When the oil in theoverlying and underlying beds is progressively displaced by heatedwater, the oil is recovered in a more efficient manner than if the oiland water were at normal` formation temperature before contacting theheated zone as in a countercurrent liow of liquid and air in theparallel zones. Additionally, the areal sweep eiliciency of the injectedwater is improved because of the inproved mobility ratio of thedisplacing water to the displaced crude oil. This ratio is progressivelyreduced as both the Water and oil are gradually heated by absorbing heatlosses from the middle strata wherein corn.- bustion is occurring, andfrom the overlying and underlying impermeable strata. Since the flow ofboth injected air and injected water produce flow in the same directionthrough all three strata, hydrocarbon fluids can be intermingled as theyare produced from all of the oil-bearing zones into the productionwells.

Further objects and advantages of the present invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

In the drawings:

FIG. 1 is a schematic representation in vertical section of a series ofoil-bearing zones separated by shale zone fluid barriers through whichan injection well and one production well penetrate to illustrate apreferred method of carrying out the invention.

FIG. 2 is a schematic representation of the thermal profiles through aplurality of producing zones such as those shown in the systems of FIGS.1 and 3.

FIG. 3 is a View similar to FG. 1 illustrating an alternative system forinjecting water and air to assist recovery of petroleum in accordancewith the invention.

' FIG. 4 is a graph illustrating the reduction of oil/ water viscosityratio with temperature increase.

As an aid to the understanding of the method of the present invention,reference is now made to the drawings, and in particular to FIG. 1. Asthere shown, our method is directed to assisting recovery of petroleumfrom an underground reservoir system comprising a plurality ofhydrocarbon containing zones including a rst or middle zone 1t) that hasboth an overlying oil-bearing zone l2 andan underlying zone 14. Both oilzones 12 and 14 are isolated from middle zone 1@ by shale members 16 and18 respectively. Further, otherr shale zones, such as 20, overlyingupper oil zones 12, and 22 underlying lower zone 14, may separate otherhydrocarbon Lproducing zones from those illustrated 'in the present'embodiment. The term earth formation is also used hereinafter to deiinesuch a Vmulti-bedded series of zones that deiine such a petroleumreservoir.

In the embodiment of the invention of FIG. 1,'all of the cil-bearingzones 10, 12 and 14 are penetrated bysa iirst well 24 indicated as anassisted-recovery injection well, and a second well 2d, operated as aproducing well. Since, in accordance with the invention, it is desiredto ignite and burn mid-zone to create' an eX- pandingv heat reservoirthat vwill drive petroleum toward well 26, a pair of packers 28 andV30are positioned lin injection well 24 respectively to isolate middlezoneV 16 from upper and lower zones 12 and 14. An air injection line V32that may include a burner 34 is positioned within the nowvisolated zone,indicated as 31, and is connected to'an air compressor 36 at the earthssurface. With zone 10 isolated in this manner, ignition and combustionof the -oil zone 1d may be initiated by supplyine fuel gas from line 38through valve 4i). After ignition of oil- I bearing zone 10, fuel gasmay be cutoff by closing valve 4i) and combustion continued merely bysupplying air Yunder pressure. The combustion front, indicated generallyas 42, is then progressively advanced toward production Well 26 adistance sulicient to establish the proper size heat bank for theparticular system being treated. This 4distance will, of course, dependupon the thickness of sand zone 10, shale members 16 and 18, the thermaldilusivity in said sand and shale members and the velocity of the burnfront. Then, with the-combustion fron-t 42 mov-ing toward producing well26, in accord-l ance withthis invention, we inject water into overlying.'As indicatedby dash lines 44 and 46 in the respective zones 12 and 14,progress of water in said zones will be v greater where the-temperatureis higher due to the de- As indicated, such creased viscosity of theheated oil. water iioodingrof zones 12 and 14 Vvis accomplished bysupplying water through line 48 discharged by water f pump 150. Across-over pipe. 52 permits water pressure 'to beappli'ed to lower zone14- through packers 28 and 30 that isolate zone 10 from the remainder ofthe Well v bore.

v Oil produced fromall of the three zones, 10, 12 and 14 is permitted tointermingle iin producing'well 26. As indicated, the outflow from thatwell is transmitted to a separator (not shown), wherein thesecondarydrive fluid may be separated 'from V'the produced oil.V

FIG. 2 in general illustrated the thermal fronts in the three adjacentzones when the .different drive fluids are flowing, as in thearrangement of FIG. 1. As indicated, the combustion front such asthatfin, middle zone 10- of FIGS. 1 and 3 will'be relatively uniform inarea and substantially vertical to the overlying and underlying uidimpermeable beds. The temperature of this Zone indicated as 1000 F.,will be in the range of from 750-1500" 'temperature suiciently great tocause heating in the area directly above and below the combustion sand.

In the art of water o'oding, the displacement eiciency of crude oil isimproved if the mobility ratio of the `dis- Vand lunderlying sand beds14 and 12. In the schematic placing water to the displaced oilrisreduced. The mobility ratio is defined as the ratio:

Relative oil permeability Y is a function of the oil and watersaturations and `the characteristicsnof the producing sand. Y Theoil/water viscosity ratio depends markedly upon temperature.

The object of the present invention is to reduce thisy mobility ratio ofthe displacing water to the displaced oil and consequently impr-ove therecovery of oil by malring use of heat normally lostin. an undergroundcombus-` tion process. FIG. 4 shows the reduction in oil/water viscosityratio as the temperature is increased from F. to y300" F. forrepresentative crude. oils. As ,an example, an increase in temperaturefrom 100 F. to 3009 F. in a system containing 15 yAPI oil will result ina thirty-fold reduction of oil/water viscosity ratio.

It is preferred to progressively advancethe burning front from theinjection well toward the production weil for a time suiiicient to heatthe adjacent upper and lower oil-impermeable zones by conduction of heatfrom said burning front and reduce the oil/water viscosity ratio 1nVboth the upper and lower oil-permeable zones, to a value less thanabout 200. Flood water is then injected through the injection well intothe upper and lower producing zones to successively absorbheat romsaidoil impermeable zones. Air 4and flood water are simultaneously pumpedinto the respective zones to advance both the water and oilV in saidzones toward said production well while maintaining said oil/waterviscosity ratio in Vsaid upper and lower oil-permeable zones at saidvalue. Qll is produced at theV production well fromV all producmg zones.Y Y

The mechanism for improved oil recovery in the adjacent water oodedsands is as follows:

First: The injected Water is heated by contact with progressively warmerenvironment as it moves toward the .position of the combustion front inthe combustion sand. Y v

Second: Oil displacement by the injection water is irnproved as theinjection water approaches progressively warmer oil in theoil-bearingsands in which wateris injected. The displacement of oil by water 1s amaximum where theo'il reaches a'maximum temperature and mlmmumviscosity. This point will always be behind the position ofthercombustion front but will vary, depending upon .the system in whichthe process is applied.

It is, of course, understood that displacement of. oil by water in awater-ooding operation is not strictly a piston-like displacementwherein equal amounts of formation oil are displaced by a correspondingvolume of the driving Water. Rather, the displacement is effected byein.` trainrnent of oilparticles released from the-interstitial spacesin the oil reservoir by water flowing pasty these spaces. Hence, reducedviscosity of reservoir oil as compared to the entraining water greatlyVincreases the eiciency'of oilY displacement by the injection of water.

However, the freedom of the oil particles to enter the -llood Water isalso dependent upon the relative sizes andV .9 from the injection wellsto the production wells to reduce the possibility of such channeling.

In FIG. 2, the general temperature profiles of a progressingmulti-bedded fire and water flood in a system such as that shown in FIG.l are illustrated by the isotherm lines, designated as 100 F., 200 F.,etc. In the example illustrated by FIG. 2, the thickness of the burnedmiddle sand is about 10 feet, the thermal diffusivity is about 0.05square feet per hour, the burn front velocity is about 0.5 feet per day,and the maximum burn front temperature is 1000 F. The temperaturesindicated represent increases over original reservoir temperatures. Itwill be noted that the maximum temperature extends over quite a limitedarea, but an increase in temperature of from 100 F. to 300 F. is quitebroad through both of the adjacent sands.

FIG. 3 illustrates an alternative arrangement for carrying out themethod of the present invention, wherein separate wells are used for theinjection of air and Water into the selected oil-bearing sands. Asindicated, well 64 is drilled into middle sand It) and has an air supplyline 32 that supports a burner 34 opposite that zone to start combustionof the residual petroleum therein. As shown, well 6d may be cemented oiat bottom 66 above lower producing zone 14. Zone 10 and well 64 are alsoisolated from upper zone l2 by cement 72 located adjacent upper shalesection 16. Perforations 68 through casing 65 and cement 72 permitcommunication between zone 10 and well 64. It will be noted that airinjection well 64 is positioned ahead of water injection well 70 so thatcombustion may be started and extended both vertically and horizontallyin middle zone l prior to the time the combustion front passes throughwell 70. Communication between well 70 and middle zone l0 is preventedby cement 72 that bridges between casing 7l and upper and lower shalemembers 16 and 18. Perforations 74 opposite both zones 12 and 14 permitaccess through casing 71 for well 70.

As further shown in the embodiment of FIG. 3, combustion in the middlezone lil is desirably stopped some distance from production well 26 toprevent well damage. The approach of the combustion front can bedetected by a thermocouple 80 positioned in producing well 26 adjacentto, or opposite, oil-producing zone l0. Thermocouple 80 disconnectspower to drive motor 92 and air compressor 36. For this purpose, lines82 and S4 from thermocouple 80 energize sensitive relay 86 when thetemperature in the well reaches a preselected value. This controls, inturn, circuit breaker 90 through switch 88 to cut off power for aircompressor 36. Thus, when the temperature of the produced fluid in zonereaches the preselected value, the combustion process dependent upon airis automatically stopped. After such a temperature value is produced influid flowing out of middle zone l0, it may be desirable to inject waterinto the middle zone, as well as into the upper and lower producingzones 12 and 14. Thus, further maximum thermal economy can be obtainedin assisting recovery from the reservoir. An estimate of flow rates canalso be used lto determine the proper time to stop air injection in zonel0. For this purpose a ilow meter and integrating system can besubstituted for thermocouple 80.

In each of the systems shown in FIGS. l and 3, it is, of course,desirable to maintain sutlicient pressure in middle zone 10 to preventbackflow of oil or water from the producing horizons l2 and 14 due tohigher pressures that may exist in said producing sands. This backowafter combustion ends can be eliminated by injecting low volumetricrates of water, air or gas into middle zone l0 at the injection wellsuch as 24 in FIG. l, and e4 in FIG. 3.

The present method, of course, maybe used either in a line drive systemor a five spot, or circular, pattern of the injection and producingwells. A line drive system is one in which a plurality of injectionwells are drilled into the formation along a line, such as the edge, ofa producing iield, or a geological fault, so that the produced oil isdriven toward a similar line or pattern of producing wells at a distanceselected to permit maximum recovery of oil from multiple producinghorizons. On the other hand, a live spot, or circular, pattern of wellsfor assisted oil recovery is one where the injection well is in thecenter of a plurality of producing wells that are radially spacedoutwardly from the injection well. In either of such systems, thecombustion front is moved progressively outward from the injection welltoward the producing well, and progressively with said lateral movementat least one adjacent and parallel producing horizon is ooded by anysecondary drive iluid, including water containing other miscible orimmiscible materials, that will progressively absorb heat from thethermal bank or reservoir. Then, the heat is carried vertically andoutwardly from said heat bank to the liquids in said adjacent formationby conduction and by lthe drive fluids flowing therethrough.

It will be apparent to those skilled in the art that the present systempermits an appreciable increase in eciency of assisted recovery from amulti-bedded oil-producing reservoir stratified by impermeable horizons.Greater use of the thermal energy supplied by the compressed air and theburned oil in one zone is utilized to improve progressively the waterood eiiiciency of the adjacent oil-producing beds. Various changes inthe method of injecting and recovering fluids in multi-bedded reservoirsand arrangements for positioning injection and production wells willoccur to those skilled in the art. All such modications or changesfalling within the scope of the appended claims are intended to beincluded therein.

We claim:

l. The method of assisting recovery of oil from an underground reservoirthat includes at least a pair of substantially parallel, permeablehydrocarbon fluid producing z-ones separated by a relatively thinfluid-impermeable zone and said reservoir having at least an injectionWell and a production well penetrating all of said zones which comprisesthe steps of initiating combustion of said hydrocarbon fluid in one ofsaid uid producing zones adjacent said injection well, said one zonehaving greater permeability to lluid ilow therethrough than the other ofsaid pair of producing zones, injecting air through said injection wellinto said one zone to establish combustion of said hydrocarbon fluid andto extend the burning area vertically -across the thickness of said onezone to form a burning front, continuing said airV injection to maintainsaid combustion burning front and to advance it progressively a distancetoward said production well greater than the thickness of said one oilproducing zone whereby the adjacent thinner oil-impermeable zone isprogressively heated by conduction from said burning front to form aheat reservoir for said other adjacent uid producing zone, theninjecting water through said injection well into said other producingzone to permit heat from said oil-impermeable zone to be absorbedprogressively therein as said water ows concurrently with saidcombustion burning front, and continuing to inject said air and Water,respectively, to simultaneously and progressively move through saidproducing zones and assist recovery of oil from both of said producingzones into said production Well.

2. The method in accordance with claim l wherein other production zonesare parallel to said pair of oil producing zones and separated therefromby other relatively thin Huid-impermeable zones, and wherein combustionis initiated and maintained in at least the middle fluidproducing zoneby injecting air therein through an injection well and water is injectedunder pressure through said injection well intoboth the overlying andunderlying producing zones, said Water moving concurrently with saidcombustion to assist recovery of oil from said production zones.

f, 3. The method of assisting recovery of oil from an undergroundreservoir that includes at least three substantially parallel permeablehydrocarbon fluid-producing zones, each of said fluid-producing zonesbeing separated by a relatively thin u-id-imperrneable zone, and saidreservoirhaving at least one injection well and at least one productionwell penetrating said zones which com-V thereinto for a timesuiiicientprogressively to 'force hydrocarbons to il'owfromsaid zone into said atieast one Y production weil and-to-signiiicantly increase thetemperature of the adjacent oil-impermeable zones by thermal conductionfromsaid combustionffront, then introducing tlooding waterthroughv saidinjection well into the upperV and ylower yfluidproducing zones toconduct heat Ystored in said fluid-impermeable zones to the tluids insaid'upper'land lower fluid producing zones, said water advancingsubstantially in `the' Vsaule direction as saidfad- VVancing combustionfront and continuingsupply of both air and water, respectively, to allof said producing zones to simultaneously andprogressively move throughsaid producingzonesland assist recovery ofoilsimultaneously from allofsaid zones in said production wel-i. Y Y 4. The lmethod Yof assistingrecovery of oil from an underground reservoir that includes at least apair of t substantially parallel, permeable oii producing zonesseparatedy by a relatively thin iiuid impermeable zone and saidrcservoirhaving at least a production -well penetrating all of Vsaidzones and at-leastonc injection well perzones by conduction of heat fromsaid burning front and l mitting separate communication betweenearthssu-rface and said pair of oil producing zones which comprises thesteps vof initiating combustion'of a portion of the oil in one Vof saidproducing'zones adjacent'said injection Well, saidonerzone havingAgreater permeability to filuid ow therethrough than the other of saidpairiof oil producing zones, injecting air `.through said-injection wellinto said one zone-toextend combustion of 'said-oil vertically acrosstheV thickness of said `orte-zone to form aburningvfront, continuing airVinjections through said injection well lto progressively advance saidburning front yfrom said injectionwell toward said-productionwellforat'ime sufcient toreduce theoilwaterviscosityuratio to a value .lessthan` about 200, then introducing water through said injection well intosaid other producing zone to absorb heat from v saidoil-impermeable'zone, said water advancing in the same direction lassaid burning front and continuing to pump said Vair Vand water,respectively, to assist` recovery of oil simultaneously andprogressively from both of said recovery of oil from at least two of theoil-producing zones, said multibedded reservoir including at least threesubstantially parallel, permeable oil-producing zones separatedby-relatively thin Huid-impermeable zones and said reservoir having aproduction Well penetrating said zones and at least one injection wellpermitting simultaneous but separated communication between the earthssurface and Vtherniddle zone and Vbetween the earths surface and theother oil-producing zones which comprises the steps of initiatingVcombustion of a portion-of the oil in the middle zone adjacent to saidinjection well, injecting air through said injection well into saidmiddle zone to extend combustion of said oil vertically across thethickness ofrsaid middle zone -to form a burning front, progressivelyadvancing said burning front from said injection well toward saidproduction well for a time sutiicient'to heat the adjacent upper andlower oil-impermeable permeable V,zones at said value, andsimultaneously pro- 1 ducing oil into said production Well from allofsaid producing zones.

References Cited inthe tile of this patent UNITED 4STATES PATENTS2,584,605` Merriam et al. Feb. 5, 1952 t 2,734,579 Elkins Feb. 14, 19562,788,071 Pelzer Apr. 9, 1957 2,901,043

Y Campion et al. Aug. 25, 1959

1. THE METHOD OF ASSISTING RECOVERY OF OIL FROM AN UNDERGROUND RESERVOIRTHAT INCLUDES AT LEAST A PAIR OF SUBSTANTIALLY PARALLEL, PERMEABLEHYDROCARBON FLUID PRODUCING ZONES SEPARATED BY A RELATIVELY THINFLUID-IMPERMEABLE ZONE AND SAID RSERVOIR HAVING AT LEAST AN INJECTIONWELL AND A PRODUCTION WELL PENETRATING ALL OF SAID ZONES WHICH COMPRISESTHE STEPS OF INITIATING COMBUSTION OF SAID HYDROCARBON FOUID IN ONE OFSAID FLUID PRODUCING ZONES ADJACENT SAID INJECTION WELL, SAID ONE ZONEHAVING GREATER PERMEABILITY TO FLUID FLOW THERETHROUGH THAN THE OTHER OFSAID PAIR OF PRODUCING ZONES, INJECTING AIR THROUGH SAID INJECTION WELLINTO SAID ONE ZONE TO ESTABLISH COMBUSTION OF SAID HYDROCARBON FLUID ANDTO EXTEND THE BURNING AREA VERTICALLY ACROSS THE THICKNESS OF SAID ONEZONE TO FORM A BURNING FRONT, CONTINUING SAID AIR INJECTION TO MAINTAINSAID COMBUSTION BURNING FRONT AND TO ADVANCE IT PROGORESSIVELY ADISTANCE TOWARD SAID PRODUCTION WELL GREATER THAN THE THICKNESS OF SAIDONE OIL PRODUCING ZONE WHEREBY THE ADJACENT THINNER OIL-IMPERMEABLE ZONEIS PROGRESSIVELY HEATED BY CONDUCTION FROM SAID BURNING FRONT TO FORM AHEAT RESERVOIR FOR SAID OTHER ADJACENT FLUID PRODUCING ZONE, THENINJECTING WATER THROUGH SAID INJECTION WELL INTO SAID OTHER PRODUCINGZONE TO PERMIT HEAT FROM SAID OIL-IMPERMEABLE ZONE TO BE ABSORBEDPROGRESSIVELY THEREIN AS SAID WATER FLOWS CONCURRENTLY WITH SAIDCOMBUSTION BURNING FRONT, AND CONTINUING TO INJECT SAID AIR AND WATER,RESPECTIVELY, TO SIMULTANEOUSLY AND PROGRESSIVELY MOVE THROUGH SAIDPRODUCING ZONES AND ASSIST RECOVERY OF OIL FROM BOTH OF SAID PRODUCINGZONES INTO SAID PRODUCTION WELL.